Physics Imaging

Question 1

What are the clinical imaging techniques commonly used and which one is the cheapest and quickest?

Answer 1

X-ray
Ultrasound (cheapest and quickest)
CT scan
MRI
PET

Question 2

What are the risks of a CT scan?

Answer 2

Ionize radiation and cancer

Question 3

What is the risk of a PET?

Answer 3

Allergic reaction to tracers, unsuitable for pregnant or breast feeding patients.

Question 4

What are the risks of an MRI?

Answer 4

Claustrophobia and unsuitable for patients with metal implants

Question 5

What are the risks of an x-ray?

Answer 5

Ionizing radiation and risk of cataracts, skin reddining and hair loss years later

Question 6

How do Xrays and CT scans work?

Answer 6

Electromagnetic radiation which is absorbed by all tissue and the extent of this absorption depends on density of the tissue (bones absorb more energy). They areionisingradiation.

Question 7

How do MRI’s work? (LONG)

Answer 7

They create magnetic feilds round the patient causing the bodies hydrogen atoms to align with the feild. Radio signals are sent into the body can cause the atoms to resonate taking energy from the signal and spinning out of equilibrium. When the field is turned off, sensory detect energy release and time to equilibrium. This signal can be used to see detailed images of the body as all body tissue has different levels and density of hydrogen atoms.

Question 8

How does PET imaging work?

Answer 8

Gamma imaging technique where radiotracers emit positrons. These positrons meet electron in patients body and you get annihilation results in 2 gamma-rays. Gamma-rays which do not appear in pairs are disregarded.

Question 9

How do ultrasounds work?

Answer 9

An ultrasound transducer emits an ultrasound beam which bounces of any tissue creating an image on a screen. The transducer needs gel as it is sensitive enough to reflect off air and this stops air from getting to it.

Question 10

What is the frequency of ultrasounds, clinical ultrasounds and why are they used?

Answer 10

Ultrasound frequencies detect acoustics over 20kHz and clinical ultrasounds detect between 1MHz and 20MHz. These help highlight tissues and higher acoustics are used in preclinical trails as these do not need to see depth just clear images.

Question 11

What techniques does the ultrasound transducer use and what is it made off?

Answer 11

Is made up ofpeizoelectriccrystals focusing beam into the tissue. The transducer uses pulse echo techniques which travels at a constant speed of 50/40metresper second and is reflected back and you can see it

Question 12

How do you see brightness using longitudinal waves?

Answer 12

The pulses hit a particle (tissue) and some of it is reflected back into the transducer and some continues on into the body. The amplitude of the reflected pulse if seen as brightness. The bigger the particle (tissue) the bigger the amplitude and therefore the brightness.

Question 13

How do you work out longitudinal wave?

Answer 13

You work this out using Z = C x P

With: Z = the acoustic impedance, C = speed of sound and P = density of material.

Question 14

What is M mode?

Answer 14

you separate out the ultrasound scanner and this is used to see better temporal images.

Question 15

Why use an ultrasound?

Answer 15

Look at size and depth of something, ultrasound operated injections, age of fetus, radiology (how healthy organs look), echocardiography

Question 16

What are therapeutic microbubbles and how would they be used?

Answer 16

There is a concept of putting drugs into the shell and released by destroying the bubble at the required location. You would need ultrasound to locate thetumourand place the drugs correctly next to it.

Question 17

Why would you use therapeutic microbubbles?

Answer 17

You can use microbubbles tocharacterisedrug loading, respond to US mediated drug release and uptake and target drug release PK/PD response,

Question 18

BBB example?

Answer 18

Open the blood brain barrier (BBB) using ultrasounds which normally prevents most things including drugs from getting through. They want to open this up so they can get drugs in

Question 19

What can you use a PET scanner for?

Answer 19

Imaging modalities include functional and structural imaging. Structural includes CT scans whereas PET scans are functional. Ultrasound and MRI’s can do both

Question 20

How does a PET scan work?

Answer 20

You have a compound of interest and a radioisotope to make a radiotracer.

The compound of interest could be anything – cells, peptides, proteins etc.

Question 21

What can PET scans look for when quantifying molecular processes in vivo and non-invasively?

Answer 21

This can look at surface receptors, glycolytic rate, hypoxia, membrane synthesis, protein synthesis, enzymes, drug transport, angiogenesis, blood flow/perfusion, nuclear receptors and proliferation rate.

We can do both highly specific and selective imaging but also wide images.

Question 22

How does PET imaging work?

Answer 22

A radiotracer is injected into research subject andbiodistributesin research subject. The radioactive nucleus decays and releases 2 gamma photons which are detected by camera. Images showing the radiotracer biodistribution in subject body are obtained. The more metabolic the organ the more clearly it is seen as more of the radiotracer is shown.

Question 23

What is the physics behind PET scans?

Answer 23

The radioactive nucleus labelling the cells is unstable and decays into a positron. This positron travels through matter, loses energy and slows down. Positrons encounters electrons and annihilates them resulting into 2 gamma photons. This is detected by the PET detector which circulates the patient.

Question 24

Can you combine PET imaging?

Answer 24

Yes with CT or MRI in order to get both structural and functional imaging.

Question 25

Why would you use PET scans to incorporate molecular imaging to include or exclude people from drug clinical trials?

Answer 25

It can be used as a way to select the correct patients for the trial for
It can be used to look for the correct dose

Question 26

What is total body PET scans and why is this good?

Answer 26

Total body scans

Is good as it reduces time you are in the scanner, it increases sensitivity which means not as much radiation is needed

Question 27

What are the challenges of a whole body scanner?

Answer 27

The challenges of this however is the process and analysis of big datasets.
Kinetic modelling for multiple-organ analysis is also harder
You will also have to deal with multi-organ data mining.

Question 28

Can you use PET personalised medicine?

Answer 28

Yes - the radiotracers will be personalised for one person

Question 29

Why are they struggling to analyse PET’s?

Answer 29

we went from 2d images to 3d images. They set up SUV at this point (Standardised, Uptake, Value) to quantify the signal which isnormalisedfor body weight and drug dose.

We are now doing kinetic modeling – this involves looking at ligands and ligand receptor complexes which we can measure using dynamic imaging. We can calculate the parameters and map it.

Question 30

Are we going to be able to see chemical changes by scans and no longer need to take blood?

Answer 30

Yes

Question 31

Are they trying to identify macrophages and therefore inflammation?

Answer 31

Yes which is good as it can stop serious inflammation e.g sepsis before it happens

Question 32

Can we do multi organ kinetics?

Answer 32

Yes but this involved awful calculations that we dont need to know

Question 33

What oppertunities does total body PET produce?

Answer 33

Can use total body PET to derive input function which is good as you need no more arterial blood.

Can assess multiple system at once but different kinetics makes analysis hard.

Can learn about different organ system work together but parametric mapping with models are challenging and insufficient.